There was a chance of afternoon rain in the forecast as thousands of fans settled in for the start of the landmark stock car race.
At least 28 spectators were injured Saturday when a race car broke apart on the track in the midst of a 13-car wreck and sent parts and debris flying into the stands.
USA Today said the conditions of two critically injured fans, including a child, were upgraded Sunday. Their new status was not announced.
Track workers toiled through the night repairing the damaged fence in anticipation of a 1 p.m. EST start for the 500 with Danica Patrick sitting on the pole.
The (Daytona Beach, Fla.) News-Journal said NASCAR officials were also eyeing a line of thunderstorms moving into the area. Skies were overcast leading up to the start and the National Weather Service pegged the chance of afternoon rain in the Daytona Beach area at 50 percent.